This invention relates to axle suspension systems for wheeled vehicles. More particularly, this invention relates to lift axle suspension systems used as auxiliary systems on vehicles already having a non-lift axle suspension as its primary means of support.
Lift axle suspension systems have been used in the medium and heavy-duty trucking industry in this country, on a regular commercial basis, for approximately three decades. Two of the earliest, successful, and reliable lift axle suspension systems were produced by the Neway Corporation and the Granning Corporation. These suspensions employed as the lifting mechanism an expandable and retractable air bag system, such that one air bag would be expanded to lower, while another air bag would be expanded to raise the auxiliary wheels from the road surface. While these systems found, and still do find, commercial acceptance, they are limited in their application primarily because of their bulk and design, which either prohibits use in a certain location or requires rearrangement of other components on the vehicle, in order to accommodate their structure. Neither system, furthermore, automatically lifts or normally biases the axle from the road surface. Rather, the position of the axle is dependent upon the inflation of an air bag system and the retention of air in that system. Accidental loss of air, such as would occur during air bag puncture, can result in the system dropping, by gravity, to the road surface or staying on the road surface if originally there.
An early attempt at providing an upward biasing means to automatically lift and normally hold the wheels off of the road surface may be found in U.S. Pat. No. 3,093,388. The device shown in that patent has found little or no commercial use or success. It comprises a series of coil springs located across the rear of the axle, adapted to what is known in the industry as the "Neway" beam-type "air-ride" suspension system. In order to provide the lifting mechanism in this patent, both coil springs and a torque bar running laterally across the vehicle are used. A shock absorber is employed, as well as air bags located at one end of the beam. Both the coil springs and torque bar required for lifting would often interfere with other mechanisms on the vehicle, such as if the suspension were to be located in the "pusher" (i.e. ahead of the drive axle and forwardly extending drive shaft). The coil springs are connected in such a manner in this design, furthermore, as to raise serious concerns as to their reliability under actual rugged operating conditions.
A major breakthrough in the lift axle suspension art was experienced with the advent of the invention found in U.S. Pat. No. 3,285,621. As shown in the drawings of that patent, a semi-elliptic leaf spring is connected at its ends to the frame member of the vehicle. Juxtapositioned between this spring and the frame of the vehicle, is an expandable and retractable air bag system. The multi-leaf leaf spring normally biases the axle off of the road surface, the axle being connected intermediate the ends of the spring. When the air bag system is expanded, it pushes down against the upward bias of the leaf springs, placing the wheel in road engaging position. Upon release of the air, the wheels are automatically returned by the leaf spring bias to their lifted position. By the use of this simple, yet uniquely synergistic design, a new dimension in lift axle suspension systems was created. Commercial success was virtually immediate and continues to this day.
The system shown in this patent can be ubiquitously used in all positions on the vehicle, particularly in the important and safe position known as the "pusher" position, as described above. This is because the lifting mechanism, namely, the longitudinally extending leaf springs, are located adjacent the frame members of the vehicle, thus presenting no interference problem with the drive shaft, etc., of the vehicle. In addition, air bag puncture (or other air loss) results in automatic lifting of the failed system from the road surface. Still further, since the leaf springs are non-load bearing, they can be designed to be of lesser weight, yet still serve the important safety features of stabilizing and shock absorbing.
While the invention disclosed in U.S. Pat. No. 3,285,621 continues to remain a highly effective system, it has been recognized in recent years that the use of a semi-elliptic leaf spring connected at its ends to the frame of the vehicle, can at times be a drawback--prohibiting its use on certain modern, medium and heavy-duty trucks whose frame lengths and componentry can not easily accommodate, if at all, the semi-elliptic spring. It has also been recognized, with the advent of higher load carrying capabilities in modern trucks, that the unit illustrated in the aforesaid patent must be modified to accommodate these higher load bearing requirements.
Exemplary of various improving modifications made in later years to the basic invention of U.S. Pat. No. 3,285,621, are those found in:
U.S. Pat. Nos. 3,617,072, 3,730,549, 3,877,718, 3,861,708, 3,902,734, 3,904,220, 4,000,913.
Among these patents is U.S. Pat. No. 3,904,220 which deals specifically with the concept of shortening the overall length characteristics of the lift axle unit illustrated in U.S. Pat. No. 3,285,621, by way of certain geometry considerations in the air bag and leaf spring system. While this concept has proven useful and commercially successful, it still employs a semi-elliptic spring, and thus, while reducing the overall length of the system, still presents a spacing problem on certain modern truck chassis designs.
Attempts have been made to employ quarter-elliptic leaf springs to achieve the benefits and characteristics of the basic unit illustrated in U.S. Pat. No. 3,285,621 and thereby, inherently, in some instances, to reduce the overall length of the system that would otherwise exist if a semi-elliptic spring were employed. Such use of quarter-elliptic leaf springs may be found, for example, in a unit known as the "Page L-25", produced at one time by the Page Division of Dura Corporation, or as another example, in U.S. Pat. No. 3,751,066. Commercial examples of this latter concept include the Truckstell "Fastback" and the Bonnin and Silent Drive units (100B and "Challenger", respectively). While the first suspension employing an upwardly biased quarter-elliptic spring shortens somewhat the overall suspension design, and while the second tends to add little, if any, length to the basic "Neway" non-lift design, both require a substantial structure at the moment end of the spring in order to withstand the forces that are generated in the structure during use. Neither of these suspensions, furthermore, has proved to be anywhere near as commercially acceptable or successful as the basic semi-elliptic spring invention, and each has had some rather serious reliability problems reported in association therewith.
In recent years, the upwardly biasing coil spring concept suggested first in U.S. Pat. No. 3,093,388 discussed above, has been modified to make it more commercially acceptable and reliable, thereby to achieve relatively compact lift axle suspension designs used in tight vehicle frame situations. An example of such a modification is the "Neway" coil spring suspension (ARTA-5000 Series) which requires a somewhat elaborate mechanism for retaining the spring, and adds only a small amount of additional length to the basic non-lift Neway suspension. E-Z Ride (Harsco Corp.) and Dura Corp. have also marketed coil spring lift axle suspension systems which have achieved relatively compact dimensional characteristics, but which, like the others, employ coil springs, and thus, retain certain drawbacks inherent in their use (e.g. perceived lower reliability, less stability, no interleaf shock-absorbing friction, etc.), and which have never enjoyed the commercial acceptance of the leaf spring concept.
From the above, it can be seen that there currently exists a need in the art for a reliable, and yet effective, lift axle suspension mechanism which has the unique advantages of a leaf spring suspension, but which, at the same time, avoids not only the problems associated with the coil spring mechanism, but also with the length problems involved in using a semi-elliptic leaf spring, as well as the structural problems associated with using a quarter-elliptic spring.
It is the purpose of this invention to fulfill this and other needs which will become more apparent to the skilled artisan, once given the following disclosure:
Generally speaking, this invention fulfills the above-described needs by providing in a lift axle suspension system for a frame-membered wheeled vehicle, including normally upwardly biasing means for raising a wheel-bearing axle of the vehicle from the road surface, and means for lowering the wheel-bearing axle into road surface engagement by acting against the normal bias of the normally upwardly biasing means, the improvement comprising as the normally upwardly biasing means, a first and second leaf spring connected at one of their ends to each other, the first leaf spring having its opposite end connectable to the frame of the vehicle, and the second leaf spring having its opposite end connectable to the wheel-bearing axle.
By providing such a suspension system, particularly in the preferred embodiments where the two leaf springs are back-to-back, quarter-elliptic springs, with their main (longest) leaves being directly connected to each other, the remaining leaves diverging in length as one proceeds away from the connection, accompanied by the appropriate structure, there is achieved a highly advantageous and unique lift mechanism, which when employed as the upward biasing means in a lift axle suspension system, achieves unique and synergistic results.